State four structural features of red blood cells and, for each feature, explain how it helps in the transport of oxygen.

Cambridge International IGCSE Biology (0610) — 9.4 Blood · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Haemoglobin – binds O₂, carrying it in the blood.
2. Biconcave shape – gives a large surface area/volume ratio, speeding O₂ diffusion.
3. Anucleate – frees space for more haemoglobin, increasing O₂ capacity.
4. Small, flexible – can squeeze through capillaries, delivering O₂ to all tissues.

Examiner tips

Use the exact terms: haemoglobin, anucleate, biconcave, flexible. Link each feature directly to its oxygen‑transport benefit. Keep each point brief – one sentence per feature is enough for 4 marks.

Common mistakes

Writing ‘no nucleus’ instead of ‘anucleate’. Forgetting to explain the benefit of each feature. Using vague phrases like ‘good shape’ without mentioning surface area.

Mark scheme (4 marks)

Red blood cells contain haemoglobin, which binds to oxygen for transport.
Red blood cells are biconcave in shape, giving a large surface area relative to volume, increasing the rate of diffusion of oxygen into and out of the cell.
Red blood cells have no nucleus (are anucleate), leaving more space for haemoglobin so more oxygen can be carried.
Red blood cells are small and flexible, allowing them to pass through narrow capillaries so oxygen can be delivered to all tissues.

Key terms in this question

red blood cell